While more generically applicable, cross-loop antennas have been finding increased popularity in radio navigation applications, such as Loran-C pulse radio location and tracking systems.
The Loran-C magnetic cross-loop type of antenna consists of four coils wound in two orthogonal pairs on a ferrite cross as described in the above-mentioned patents, and as hereinafter shown in FIG. 1.
Without tuning, the Loran-C H-field generates voltages of the same phase across the four coils and of amplitudes depending upon the angular orientation of the cross-loop antenna with respect to the H-field. These induced voltages do not cause any navigation position errors.
To increase the signal strength, however, these coils are usually tuned to the Loran-C frequency ωc by means of capacitors shunting the coils. When the coils are so tuned to the carrier frequency, however, circular currents are generated in the four tuned circuits, and these currents have both in-phase and quadrature components. The quadrature current components, moreover, cause a shift in the antenna current zero crossings and consequently cause deleterious navigation position errors. Such errors must be eliminated in order to make such a loop antenna useful in applications such as in radio signal navigation. The present invention is directed to the effective elimination of such quadrature current components and such errors with simple apparatus.